title: Hypoxia and HIF-1 suppress SERCA2a expression in embryonic cardiac myocytes through two interdependent hypoxia response elements.
abstract: Sarcoplasmic reticulum (SR) Ca(2+)-ATPase (SERCA2a) is an essential component of cardiomyocyte excitation-contraction (EC)-coupling. Suppression of SERCA2a expression induces contractile dysfunction and has been reported in various forms of ischemic cardiac disease as well as in hypobaric hypoxia. The present study investigated whether SERCA2a expression is regulated by hypoxia in embryonic mouse cardiomyocytes and explored the underlying mechanism. We show that in cultured embryonic cardiomyocytes hypoxia (1% O(2)) induce time-dependent downregulation of SERCA2a expression. This mechanism manifested as specific changes in cardiac myocyte calcium signals induced by reduced expression and activity of SERCA2a. Chemical activation of hypoxia-inducible factor-1 (HIF-1) by DFO or overexpression of normoxia-stabile HIF-1α (HIF-1α/VP16) suppressed endogenous SERCA2a expression as well as the activity of the SERCA2a-promoter-luciferase reporter. Analysis of the SERCA2a promoter found two putative HIF-1 binding HRE-sites. Site-specific promoter mutagenesis revealed that co-operative HIF-1 binding to both of these hypoxia response elements on the SERCA2a promoter is required for expressional suppression. This mechanism establishes a link between oxygen supply and calcium activity in embryonic cardiac myocytes that is exploited in cardiac development, and further may offer a possible explanation for the functional depression of SERCA2a seen in ischemic and hypoxic myocardium.
authors.affiliation: Department of Physiology, Institute of Biomedicine and Biocenter Oulu, University of Oulu, FI-90014 Oulu, Finland.
authors.forename: Veli-Pekka
authors.initials: VP
authors.lastname: Ronkainen
authors.forename: Reka
authors.initials: R
authors.lastname: Skoumal
authors.forename: Pasi
authors.initials: P
authors.lastname: Tavi
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002118:Calcium / Q000378:metabolism; D015687:Cell Hypoxia; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D023061:Gene Order; D017405:Herpes Simplex Virus Protein Vmw65 / Q000235:genetics / Q000378:metabolism; D051793:Hypoxia-Inducible Factor 1 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D032383:Myocytes, Cardiac / Q000201:enzymology*; D010100:Oxygen / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D021381:Protein Transport; D020218:Response Elements / Q000235:genetics / Q000502:physiology*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D012689:Sequence Homology, Nucleic Acid
chemical_list: D017405:Herpes Simplex Virus Protein Vmw65; D051793:Hypoxia-Inducible Factor 1; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D010100:Oxygen; D002118:Calcium